1. Field of the Invention
The invention relates to a method of controlling automatic state returns for a dynamic system coupled to automatic control means operating in the discrete feedback mode, the method comprising a defining phase for defining the automatic control means and an operation phase for operating the system, the defining phase being an open loop learning phase which comprises a step in which states are read in which the system may be situated, and a step in which commands are generated, these commands being used for correcting errors measured between the states and an ideal state.
The invention likewise relates to an apparatus comprising a control system coupled to automatic control means defined by the method. The invention also relates to a controller defined by the method for realizing the automatic control of such apparatus.
The system may be a hard disk of a computer or, more generally, a system for recording and reproducing data or signals, for example, audio or video signals.
2. Description of the Related Art
European Patent Application EP 0 598 594 describes a controller for a disk drive system. The controller moves a read/write head relative to the tracks of the disc as a function of a predetermined velocity profile. If the desired profile is not adhered to, the controller produces commands for correcting the differences observed. This controller utilizes the fuzzy logic technique for effecting these corrections. These corrections are shown in the form of fuzzy rules which are stored in devices suitably used while the system is being operated. Such a system may adopt various states, one state being defined by a state vector in which various parameters selected according to the type of the system, or according to the control, one wishes to effect. Thus, one may wish to prefer a control of the velocity of the read/write head as in cited document, or carry out a control of the position of the head relative to the tracks of the disc, or any parameter or any other parameter association. In the case of a hard disk, if the read head is not correctly positioned on the track of the disc, either the read/write operation is stopped, or the head is returned to the center of the track. The problem posed then consists of returning the system, situated in a defective state, to an ideal state for which the errors relating to each parameter are zero or at least very small, the errors being measured between the real state of the system and the ideal state.
In a general manner, the control systems may be linear or non-linear. The linear controllers, such as the PID controllers (Proportional Integral/Differential Control), may be ill-adapted to a control of such systems. A PID controller is a linear controller which realizes a linear combination of the terms P, I and D. Such a linear controller provides an approximation which is not always satisfactory and, therefore, leads to errors which may adversely affect the precision of the controller.
Nevertheless, there are approaches utilizing non-linear controllers, but they are generally very hard to use, so that often mediocre automatic control qualities are the result.